A so-called easy-open end has heretofore been extensively used as a container end that can be easily unsealed by hand without using any particular utensil. From the standpoint of workability, the container end is obtained by using a resin-coated metal sheet which has a resin coating such as polyester film applied onto a surface-treated steel plate such as tin plate or TFS, or an aluminum alloy as a metal blank, by providing the container end of the metal sheet with a score extending on the way in the direction of thickness of the metal plate to sectionalize the portion for forming an opening, by forming a rivet by using the end sheet itself in the portion for forming the opening, and by fixing a pull tab by the rivet. The container end is double-seamed with a flange such as a can body member.
The easy-open end using an aluminum alloy sheet is, usually, advantageous from the standpoint of workability and retaining flavor accompanied, however, by a problem of inferior corrosion resistance to that of the surface-treated steel members. Therefore, the aluminum alloy sheet has heretofore been treated for its surfaces chiefly with chromic phosphate. However, the solution used for the treatment with the chromic phosphate contains hexavalent chrome which is a harmful substance. From the environmental point of view, therefore, it has been desired to conduct a surface treatment that substitutes for the treatment with the chromic phosphate.
In order to solve the above problem, various resin-coated aluminum sheets have been proposed being subjected to the non-chromium type surface treatment. For example, JP-A-2005-126097 is proposing a resin-coated aluminum alloy sheet forming an organic/inorganic composite surface-treating layer containing a zirconium compound and/or a titanium compound, an organic phosphonic acid compound and tannin, and coated with a polyester film via an epoxyphenol resin type adhesive primer.